I used the mobile key at the JW Marriott - Mall of America in Bloomington, MN. It worked fine in the elevator and to open my room but didn't give me access to the Executive Lounge. I went to the front desk to inquire, they supposedly added access but then the mobile key stopped working altogether. Went back to the front desk and got a new physical key which opened everything and had lounge access as well. So I would say it is a nice feature but needs some more refinement.